Signaling presence of chroma component in video bitstream

ABSTRACT

Aspects of the disclosure provide a method and an apparatus including processing circuitry for video decoding. The processing circuitry decodes, from a coded video bitstream, a first syntax element indicating whether a first component in the coded video bitstream is coded based on a second component in the coded video bitstream. The processing circuitry determines whether to decode one or more second syntax elements for a chroma related coding tool based on the first syntax element. The chroma related coding tool is a luma mapping with chroma scaling coding tool or a cross-component adaptive loop filter. The one or more second syntax elements are decoded when the first syntax element indicates that the first component is coded based on the second component. The one or more second syntax elements are not decoded when the first syntax element indicates that the first component is not coded based on the second component.

INCORPORATION BY REFERENCE

The present application is a continuation of U.S. application Ser. No.17/683,969, “METHOD AND APPARATUS FOR VIDEO CODING” filed on Mar. 1,2022, which is a continuation of U.S. patent application Ser. No.17/096,674, “METHOD AND APPARATUS FOR VIDEO CODING” filed on Nov. 12,2020, now U.S. Pat. No. 11,303,914, which claims the benefit of priorityto U.S. Provisional Application No. 62/958,694, “SIGNALING OF CHROMAPRESENT FLAG FOR SUPPORTING VARIOUS CHROMA FORMAT” filed on Jan. 8,2020. The above-listed applications are incorporated by reference hereinin their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has specific bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (180) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The processing circuitry can decode afirst syntax element from a coded video bitstream. The first syntaxelement can indicate whether a first component in the coded videobitstream is coded based on a second component in the coded videobitstream. The processing circuitry can determine whether to decode oneor more second syntax elements for a chroma related coding tool based onthe first syntax element. The chroma related coding tool is one of (i) aluma mapping with chroma scaling (LMCS) coding tool and (ii) across-component adaptive loop filter (CC-ALF). The processing circuitrycan decode the one or more second syntax elements for the chroma relatedcoding tool based on the first syntax element indicating that the firstcomponent is coded based on the second component in the coded videobitstream and the first component is a chroma component. The one or moresecond syntax elements for the chroma related coding tool are notdecoded based on the first syntax element indicating that the firstcomponent is not coded based on the second component in the coded videobitstream.

In an embodiment, the first syntax element is signaled in an adaptationparameter set (APS).

In an embodiment, the first syntax element indicates at a sequence levelwhether the first component is coded based on the second component.

In an embodiment, based on the first syntax element indicating that thefirst component is coded based on the second component, the secondcomponent is one of a second chroma component and a luma component inthe coded video bitstream. Based on the first syntax element indicatingthat the first component is not coded based on the second component, (i)the first component is the only component in the coded video bitstreamor (ii) the coded video bitstream includes at least the first componentand the second component and the first component is not coded based onthe second component. In an example, the coded video bitstream includesa first chroma component, a second chroma component, and a lumacomponent that have a chroma format of 4:4:4. The first component is thefirst chroma component. The second component is the second chromacomponent or the luma component. The first chroma component, the secondchroma component, and the luma component are coded independently fromeach other.

In an embodiment, the processing circuitry can disable the chromarelated coding tool based on the first syntax element indicating thatthe first component is not coded based on the second component in thecoded video bitstream.

In an embodiment, the chroma related coding tool is the LMCS codingtool. The one or more second syntax elements for the LMCS coding toolincludes a first LMCS parameter indicating an absolute value of avariable for LMCS chroma residual scaling (CRS). The processingcircuitry can decode a second LMCS parameter for the LMCS coding toolbased on the absolute value of the variable for the LMCS CRS beinglarger than 0. The one or more second syntax elements include the secondLMCS parameter that indicates a sign of the variable for the LMCS CRS.The second LMCS parameter for the LMCS coding tool is not decoded basedon the absolute value of the variable for the LMCS CRS not being largerthan 0.

In an embodiment, the chroma related coding tool is the CC-ALF. The oneor more second syntax elements for the CC-ALF include a first CC-ALFflag and a second CC-ALF flag. The first CC-ALF flag indicates whether afirst CC-ALF is signaled in the coded video bitstream. The second CC-ALFflag indicates whether a second CC-ALF is signaled in the coded videobitstream. The processing circuitry can decode syntax elements for thefirst CC-ALF based on the first CC-ALF flag indicating that the firstCC-ALF is signaled. The one or more second syntax elements for theCC-ALF include the syntax elements for the first CC-ALF. The syntaxelements for the first CC-ALF are not being decoded based on the firstCC-ALF flag indicating that the first CC-ALF is not signaled. Theprocessing circuitry can decode syntax elements for the second CC-ALFbased on the second CC-ALF flag indicating that the second CC-ALF issignaled. The one or more second syntax elements for the CC-ALF includethe syntax elements for the second CC-ALF. The syntax elements for thesecond CC-ALF are not being decoded based on the second CC-ALF flagindicating that the second CC-ALF is not signaled.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIGS. 9A-9G shows an exemplary sequence parameter set (SPS) raw bytesequence payload (RBSP) syntax according to an embodiment of thedisclosure.

FIGS. 10A-10D shows an exemplary picture parameter set (PPS) RBSP syntaxaccording to an embodiment of the disclosure.

FIGS. 11A-11B shows an exemplary adaptive loop filter (ALF) data syntaxaccording to an embodiment of the disclosure.

FIG. 12 shows an exemplary SPS RBSP syntax according to an embodiment ofthe disclosure.

FIG. 13 shows an exemplary SPS RBSP syntax according to an embodiment ofthe disclosure.

FIG. 14 shows an exemplary PPS RBSP syntax according to an embodiment ofthe disclosure.

FIG. 15 shows an exemplary APS RBSP syntax according to an embodiment ofthe disclosure.

FIG. 16 shows an exemplary adaptive loop filter (ALF) data syntaxaccording to an embodiment of the disclosure.

FIG. 17 shows a flow chart outlining a process (1700) according to anembodiment of the disclosure.

FIG. 18 shows a flow chart outlining a process (1800) according to anembodiment of the disclosure.

FIG. 19 shows a flow chart outlining a process (1900) according to anembodiment of the disclosure.

FIG. 20 shows an exemplary architecture of a luma mapping with chromascaling (LMCS) coding tool according to an embodiment of the disclosure.

FIG. 21 shows an exemplary LMCS data syntax according to an embodimentof the disclosure.

FIGS. 22A-22B show an exemplary ALF data syntax according to anembodiment of the disclosure.

FIG. 23 shows a flow chart outlining a process (2300) according to anembodiment of the disclosure.

FIG. 24 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 YCrCb, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PB s. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

A video source, for example, represented by a video bitstream can be asequence of pictures in a coding order (e.g., an encoding order, adecoding order). The video source (e.g., a coded picture, a sequence ofpictures) can include one or more sample arrays (also referred to ascomponents or planes), such as (1) a luma (Y) only (monochrome)component (or a monochromatic component), (2) a luma component and twochroma components (e.g., YCbCr or YCgCo), (3) a green component, a bluecomponent, and a red component (GBR, also known as RGB), and (4) arraysrepresenting other unspecified monochrome or tri-stimulus colorsamplings (e.g., YZX, also known as XYZ).

As described above, a video source can include multiple components, suchas a luma component and two chroma components (e.g., YCbCr or YCgCo),three color components (e.g., RGB), or the like. A component of a videosource can refer to a luma component (e.g., Y) or a chroma component(e.g., Cb, Cr, R, G, or B).

When a video source (e.g., a video sequence) includes multiplecomponents, the multiple components can be coded jointly, for example,coding of one (e.g., a first chroma component) of the multiplecomponents can be based or depend on another (e.g., a second chromacomponent or a luma component) of the multiple components. A chromacomponent is present in the video source (e.g., the chroma component ispresent in the jointly coded multiple components), for example, when thechroma component is coded jointly with or based on one of the multiplecomponents.

Alternatively, when a video source (e.g., a video sequence) includesmultiple components, the multiple components can be coded independently.For example, coding of one (e.g., a first chroma component) of themultiple components is not based on or does not depend on another one(e.g., a second chroma component or a luma component) of the multiplecomponents. Thus, coding of one (e.g., a first chroma component) of themultiple components is independent from another one (e.g., a secondchroma component or a luma component) of the multiple components. Themultiple components can be referred to as separately coded multiplecomponents. In an example, the separately coded multiple components arereferred to as separately coded multiple color planes or colorcomponents.

In an example, a chroma component is not present when a video sourceonly includes a monochromatic component. Alternatively, a chromacomponent is not present when multiple components in a video source arecoded independently or separately. In an example, when the multiplecomponents in the video source are coded independently, each of themultiple components can be treated as a monochromatic component (e.g., aluma component), and thus a chroma component (e.g., a chroma componentthat is coded based on one of the multiple components) is not present inthe video source. When the multiple components in the video source arecoded independently, various chroma related coding tools are not neededas each of the multiple components can be treated as a monochromaticcomponent.

In some examples, a video sequence to be encoded includes multiple colorplanes and different combinations of the multiple color planes may beencoded jointly. In an example, a color plane refers to a luma componentor a chroma component. In some applications, a video is monochromatic orcolor planes of a video are to be encoded independently, thus certainjoint color plane coding tools are not applicable. In order to supportapplications where a monochromatic plane is to be encoded or colorplanes are to be encoded independently, aspects of the disclosure canprovide syntax and semantics, for example, that are beyond VersatileVideo Coding (VCC), to disable one or more of the joint color planecoding tools when needed.

A chroma format index (e.g., chroma_format_idc) can indicate a chromasubsampling format (or a chroma format), for example, between chromablock(s) and a corresponding luma block. In an example, when the chromaformat index (e.g., the chroma_format_idc) is 0, the chroma format canbe ‘Monochrome’ corresponding to a monochrome sampling having only onesample array, which is nominally considered to be the luma array. Whenthe chroma format index is 1, the chroma format can be 4:2:0 (e.g., eachof two chroma arrays has half a height and half a width of acorresponding luma array). When the chroma format index is 2, the chromaformat can be 4:2:2 (e.g., each of the two chroma arrays has the sameheight and half the width of the luma array). When the chroma formatindex is 3, the chroma format can be 4:4:4, depending on a value of aseparate color plane flag (e.g., separate_colour_plane_flag). Forexample, if the separate color plane flag is equal to 0, the chromaformat is 4:4:4 (e.g., each of the two chroma arrays has the same heightand width as the luma array). Otherwise, the separate color plane flagis equal to 1, the three color planes can be separately processed asthree monochrome sampled pictures.

In some examples, such as in VVC, (i) coding a monochromatic videoand/or (ii) separately coding three color components of a 4:4:4 chromaformat video are supported. In order to support (i) the coding of amonochromatic video and/or (ii) the coding of three color components ofa 4:4:4 chroma format video separately, a variable (or a chroma arraytype) (e.g., ChromaArrayType) can be defined, for example, in VVC toenable or disable related coding tools. The related coding tool can beapplicable or not applicable based on whether an input video ismonochromatic and/or whether color components of the input video arerequired to be encoded separately and independently. In an example, whenthe input video is monochromatic and/or when the color components of theinput video are required to be encoded separately and independently, therelated coding tool is not applicable and thus disabled. Otherwise, therelated coding tool can be applicable and thus enabled.

In an example, such as in VVC, a value of the chroma array type (e.g.,ChromaArrayType) is assigned based on a value of the separate colorplane flag (e.g., a separate_colour_plane_flag). In an example, theseparate color plane flag (e.g., the separate_colour_plane_flag)indicates whether separately coded color planes are used. If theseparate color plane flag (e.g., the separate_colour_plane_flag) isequal to 0 indicating that separately coded color planes are not used,the chroma array type (e.g., ChromaArrayType) is set to be equal to achroma format (also referred to as a chroma subsampling format, e.g.,specified by chroma_format_idc). Otherwise, if the separate color planeflag (e.g., the separate_colour_plane_flag) is equal to 1 indicatingthat separately coded color planes are used, the chroma array type(e.g., ChromaArrayType) is set to 0.

When the chroma array type (e.g., ChromaArrayType) is 0, the input videocan be monochromatic or can have a chroma format of 4:4:4 (or 4:4:4chroma format) with separately coded color planes. In some examples, itis desirable to disable certain coding tools that are not applicable toa monochromatic video and/or to a video where each color component ofthe video is encoded as if each component is monochromatic. In someexamples, such as in VCC, one or more of the certain coding tools cannotbe disabled when the chroma array type (e.g., ChromaArrayType) is 0. Forexample, the certain coding tools include coding tools enabled by ajoint coding flag (e.g., sps_joint_cbcr_enabled_flag) that can indicatea joint coding of chroma residuals and a PPS joint offset present flag(e.g., pps_joint_cbcr_qp_offset_present_flag), respectively. The PPSjoint offset present flag can indicate whether a PPS joint CbCr QPoffset value and a joint CbCr QP offset list are present in a PPS RBSPsyntax structure.

Aspects of the disclosure provide embodiments/methods to disable somecoding tools, for example, when an input video is monochromatic, theinput video has multiple components that are coded separately (e.g.,coding of one of the multiple components is independently from anther ofthe multiple components). In an example, the input video has the chromaformat 4:4:4 with separately coded color planes.

FIGS. 9A-9G show a table of an exemplary sequence parameter set (SPS)raw byte sequence payload (RBSP) syntax, for example, from VVC.

FIGS. 10A-10D show a table of an exemplary picture parameter set (PPS)RBSP syntax, for example, from VVC.

FIGS. 11A-11B show a table of an exemplary adaptive loop filter (ALF)data syntax, for example, from VVC.

FIG. 12 shows an exemplary SPS RBSP syntax.

Referring to the table illustrated in FIGS. 9A-9G and FIG. 12 , a jointcoding flag (e.g., a sps_joint_cbcr_enabled_flag) can indicate a jointcoding of chroma residuals. The joint coding flag (e.g., thesps_joint_cbcr_enabled_flag) being equal to 0 can specify that the jointcoding of chroma residuals is disabled. The joint coding flag (e.g., thesps_joint_cbcr_enabled_flag) being equal to 1 can specify that the jointcoding of chroma residuals is enabled. When the joint coding flag (e.g.,the sps_joint_cbcr_enabled_flag) is not present, the joint coding flag(e.g., the sps_joint_cbcr_enabled_flag) can be inferred to be a defaultvalue, such as 0.

Referring to a box (910) in FIG. 9D, the joint coding flag (e.g., thesps_joint_cbcr_enabled_flag) can be signaled regardless of a value ofthe chroma array type (e.g., ChromaArrayType). Referring to boxes(1201)-(1202) in FIG. 12 , signaling the joint coding flag (e.g., thesps_joint_cbcr_enabled_flag) is dependent on the chroma array type(e.g., ChromaArrayType). When the chroma array type (e.g.,ChromaArrayType) equals to 0, the joint coding flag (e.g., thesps_joint_cbcr_enabled_flag) is not parsed, for example, in the SPSshown in FIG. 12 and can be inferred to be 0. Thus, the joint coding ofchroma residuals (e.g., joint Cb and Cr residual coding) as a chromaresidual coding is disabled to avoid a decoding process that isunnecessary.

In some examples, when a chroma component is not present in a videobitstream, a chroma present flag is signaled in a PPS, an adaptationparameter set (APS), and/or the like in order not to decode chromarelated syntax element(s). The chroma present flag can be signaled inthe PPS as a PPS chroma present flag (e.g., a pps_chromat_present_flag),in the APS as an APS chroma present flag (e.g., anaps_chromat_present_flag), and/or the like to indicate whether thechroma component is present or not in the video bitstream, such as in avideo sequence. In an example, the chroma component is present when thechroma component is jointly coded with another component (e.g., a lumacomponent, another chroma component).

The PPS chroma present flag (e.g., the pps_chromat_present_flag) canspecify whether a chroma component is present. When the PPS chromapresent flag (e.g., the pps_chromat_present_flag) equals to 1, thechroma component is present, and the chroma related syntax can bepresent in a PPS. The PPS chroma present flag (e.g., thepps_chromat_present_flag) being equal to 0 can specify that the chromacomponent is not present. A requirement of bitstream conformance can bethat the PPS chroma present flag (e.g., the pps_chromat_present_flag) isequal to 0 when the chroma array type (e.g., ChromaArrayType) is equalto 0.

The APS chroma present flag (e.g., the aps_chroma_present_flag) canspecify whether a chroma component is present. When the APS chromapresent flag (e.g., the aps_chroma_present_flag) equals to 1, the chromacomponent is present, and thus chroma related syntax(es) can be presentin an APS. The APS chroma present flag (e.g., theaps_chroma_present_flag) being equal to 0 can specify that the chromacomponent is not present and the chroma related syntax(es) are notpresent. A requirement of bitstream conformance can be that the APSchroma present flag (e.g., the aps_chroma_present_flag) equals to 0 whenthe chroma array type (e.g., ChromaArrayType) equals to 0.

To ensure there are no conflicts in the signaling of the chroma arraytype (e.g., ChromaArrayType) and the related syntax elements, the SPSRBSP syntax in FIGS. 9A-9G, the PPS RBSP syntax in FIGS. 10A-10D and theALF data syntax in FIGS. 11A-11B can be modified as shown in FIGS. 13-16. The changes are highlighted using boxes and texts with strikethroughsindicating deleted texts.

Referring to boxes (911)-(912) in FIGS. 9E-9F, the chroma format (e.g.,chroma_format_idc) being equal to 3 can refer to the chroma format of4:4:4 with the separate color plane flag (e.g., theseparate_colour_plane_flag) being 0 or 1. Thus, a SPS block-based deltapulse code modulation (BDPCM) chroma enabled flag (e.g., asps_bdpcm_chroma_enabled_flag), a SPS palette enabled flag (e.g., asps_palette_enabled_flag), and a SPS adaptive color transform (ACT)enabled flag (e.g., a sps_act_enabled_flag) that indicate chroma-onlycoding tool(s) and/or coding tools that use chroma component(s) aresignaled regardless of a value of the separate color plane flag (e.g.,the separate_colour_plane_flag). Comparing the boxes (911)-(912) inFIGS. 9E-9F and boxes (1301)-(1302) in FIG. 13 , respectively, thechroma array type (e.g., ChromaArrayType) in FIG. 13 can replace thechroma format (e.g., chroma_format_idc) in the table shown in FIGS.9E-9F, and thus a syntax “ChromaArrayType==3” in FIG. 13 can replace asyntax “chroma_format_idc==3” in the table shown in FIGS. 9E-9F. Asdescribed above, the chroma array type (e.g., ChromaArrayType) beingequal to 3 can indicate that the chroma format is 4:4:4 and the separatecolor plane flag (e.g., the separate_colour_plane_flag) is 0.Accordingly, the SPS BDPCM chroma enabled flag (e.g., thesps_bdpcm_chroma_enabled_flag), the SPS palette enabled flag (e.g., thesps_palette_enabled_flag), and the SPS ACT enabled flag (e.g., thesps_act_enabled_flag) can be signaled only when a value of the chromaarray type (e.g., ChromaArrayType) is 3 (e.g., when a chroma componentis present and the chroma format is 4:4:4). In an example, when a chromacomponent is not present, the chroma array type (e.g., ChromaArrayType)is 0, and thus the SPS BDPCM chroma enabled flag (e.g., thesps_bdpcm_chroma_enabled_flag), the SPS palette enabled flag (e.g., thesps_palette_enabled_flag), and the SPS ACT enabled flag (e.g., thesps_act_enabled_flag) are not signaled. Accordingly, flags related tochroma coding tools are not signaled when a chroma component is notpresent, and thus signaling overhead can be reduced and codingefficiency can be improved.

The PPS QP offsets (e.g., a pps_cb_qp_offset and a pps_cr_qp_offset) canspecify offsets to a luma QP (e.g., Qp′Y) used for deriving chroma QPs(e.g., Qp′Cb and Qp′Cr), respectively. Values of the PPS QP offsets(e.g., the pps_cb_qp_offset and the pps_cr_qp_offset) can be in a rangeof −12 to +12, inclusive. When the chroma array type (e.g.,ChromaArrayType) is equal to 0, the PPS QP offsets (e.g., thepps_cb_qp_offset and the pps_cr_qp_offset) are not used in a decodingprocess and a decoder can ignore the values of the PPS QP offsets.

A PPS joint offset present flag (e.g., apps_joint_cbcr_qp_offset_present_flag) being equal to 1 can specify thata PPS joint CbCr QP offset value (e.g., apps_joint_cbcr_qp_offset_value) and a joint CbCr QP offset list (e.g.,joint_cbcr_qp_offset_list[i]) are present in a PPS RBSP syntaxstructure. The PPS joint offset present flag (e.g., thepps_joint_cbcr_qp_offset_present_flag) being equal to 0 can specify thatthe PPS joint CbCr QP offset value (e.g., thepps_joint_cbcr_qp_offset_value) and the joint CbCr QP offset list (e.g.,the joint_cbcr_qp_offset_list[i]) are not present in the PPS RBSP syntaxstructure. When the PPS joint offset present flag (e.g., thepps_joint_cbcr_qp_offset_present_flag) is not present, the PPS jointoffset present flag (e.g., the pps_joint_cbcr_qp_offset_present_flag)can be inferred to be equal to 0.

A PPS slice flag (e.g., a pps_slice_chroma_qp_offsets_present_flag)being equal to 1 can indicate that a slice Cb QP offset (e.g., aslice_cb_qp_offset) syntax element and a slice Cr QP offset (e.g., aslice_cr_qp_offset) syntax element are present in associated sliceheaders. The PPS slice flag (e.g., thepps_slice_chroma_qp_offsets_present_flag) being equal to 0 can indicatethat the slice Cb QP offset (e.g., the slice_cb_qp_offset) syntaxelement and the slice Cr QP offset (e.g., the slice_cr_qp_offset) syntaxelement are not present in the associated slice headers. When the PPSslice flag (e.g., the pps_slice_chroma_qp_offsets_present_flag) is notpresent, the PPS slice flag (e.g., thepps_slice_chroma_qp_offsets_present_flag) can be inferred to be equal to0.

A PPS CU flag (e.g., a pps_cu_chroma_qp_offset_list_enabled_flag) beingequal to 1 can specify that an intra slice (e.g., apic_cu_chroma_qp_offset_subdiv_intra_slice) syntax element and an interslice (e.g., a pic_cu_chroma_qp_offset_subdiv_inter_slice) syntaxelement are present in picture headers referring to the PPS and that aCU flag (e.g., a cu_chroma_qp_offset_flag) may be present in a transformunit syntax and a palette coding syntax. The PPS CU flag (e.g., thepps_cu_chroma_qp_offset_list_enabled_flag) being equal to 0 can specifythat the intra slice (e.g., thepic_cu_chroma_qp_offset_subdiv_intra_slice) syntax element and the interslice (e.g., the pic_cu_chroma_qp_offset_subdiv_inter_slice) syntaxelement are not present in the picture headers referring to the PPS andthat the CU flag (e.g., the cu_chroma_qp_offset_flag) is not present inthe transform unit syntax and the palette coding syntax. When the PPS CUflag (e.g., the pps_cu_chroma_qp_offset_list_enabled_flag) is notpresent, the PPS CU flag (e.g., thepps_cu_chroma_qp_offset_list_enabled_flag) can be inferred to be equalto 0.

Referring to boxes (1001)-(1002) in FIG. 10C, certain PPS syntax, suchas the PPS quantization parameter (QP) offsets (e.g., thepps_cb_qp_offset and the pps_cr_qp_offset) for respective chromacomponents (e.g., a Cb component and a Cr component), the PPS jointoffest present flag (e.g., the pps_joint_cbcr_qp_offset_present_flag),the PPS slice flag (e.g., the pps_slice_chroma_qp_offsets_present_flag),and/or the PPS CU flag (e.g., apps_cu_chroma_qp_offset_list_enabled_flag), that indicate chroma relatedinformation can be signaled in the PPS RSRP syntax, for example, whethera chroma component is present or not, as shown in FIGS. 10A-10D.Referring to FIG. 14 , when the PPS chroma present flag (e.g., thepps_chromat_present_flag) is 1 indicating that a chroma component ispresent, the PPS syntax, such as the PPS QP offsets (e.g., thepps_cb_qp_offset and the pps_cr_qp_offset), the PPS joint offset presentflag (e.g., the pps_joint_cbcr_qp_offset_present_flag), the PPS sliceflag (e.g., the pps_slice_chroma_qp_offsets_present_flag), and/or thePPS CU flag (e.g., the pps_cu_chroma_qp_offset_list_enabled_flag), thatindicate the chroma related information can be signaled in a PPS RSRPsyntax. Otherwise, when the PPS chroma present flag (e.g., thepps_chromat_present_flag) is 0 indicating that a chroma component is notpresent, the PPS syntax is not signaled. Thus, coding efficiency can beimproved.

When the chroma array type (e.g., ChromaArrayType) is 0, a video sourcecan have a single component (e.g., a monochromatic component) or thevideo source can have the chroma format 4:4:4 with multiple componentsand the multiple components are coded separately or independently.Accordingly, a chroma component, for example, that is coded based onanother component is not present. Thus, when the chroma array type(e.g., ChromaArrayType) is 0, a video component can be encoded as if thevideo component is monochromatic or has the chroma format 4:4:4 withseparately coded color planes.

FIG. 17 shows a flow chart outlining a process (1700) according to anembodiment of the disclosure. Chroma QP related syntax parsing can bedisabled when the PPS chroma present flag (e.g., thepps_chroma_present_flag) is 0 indicating that a chroma component is notpresent, for example, to avoid an unnecessary decoding process. Syntaxelements including the PPS QP offsets (e.g., the pps_cb_qp_offset andthe pps_cr_qp_offset), the PPS joint offset present flag (e.g., thepps_joint_cbcr_qp_offset_present_flag), the PPS slice flag (e.g., thepps_slice_chroma_qp_offsets_present_flag), and/or the PPS CU flag (e.g.,the pps_cu_chroma_qp_offset_list_enabled_flag) can be inferred to be 0,and thus not applied in the QP derivation process in a decoder side.

In an example, the process (1700) starts at (S1701) and proceeds to(S1710).

At (S1710), whether the PPS chroma present flag is 1 can be determined.When the PPS chroma present flag is determined not to be 1, the process(1700) proceeds to (S1720). Otherwise, when the PPS chroma present flagis determined to be 1, the process (1700) proceeds to (S1730).

At (S1720), a chroma QP related syntax element, for example, one of thePPS QP offsets (e.g., the pps_cb_qp_offset and the pps_cr_qp_offset),the PPS joint offset present flag (e.g., thepps_joint_cbcr_qp_offset_present_flag), the PPS slice flag (e.g., thepps_slice_chroma_qp_offsets_present_flag), the PPS CU flag (e.g., thepps_cu_chroma_qp_offset_list_enabled_flag), and the like can be inferredto be 0. The process (1700) proceeds to (S1740).

At (S1740), the chroma QP related syntax element that is 0 is notapplied. The process (1700) proceeds to (S1799), and terminates.

At (S1730), the chroma QP related syntax element can be decoded. Theprocess (1700) proceeds to (S1750).

At (S1750), whether the chroma QP related syntax element is not 0 can bedetermined. When the chroma QP related syntax element is determined tobe 0, the process (1700) proceeds to (S1740). Otherwise, when the chromaQP related syntax element is determined not to be 0, the process (1700)proceeds to (S1760).

At (S1760), the chroma QP related syntax element that is not 0 can beapplied. The process (1700) proceeds to (S1799), and terminates.

An ALF chroma filter signal flag (e.g., analf_chroma_filter_signal_flag) being equal to 1 can specify that an ALFchroma filter is signaled. The ALF chroma filter signal flag (e.g., thealf_chroma_filter_signal_flag) being equal to 0 can specify that the ALFchroma filter is not signaled. When the ALF chroma filter signal flag(e.g., the alf_chroma_filter_signal_flag) is not present, the ALF chromafilter signal flag (e.g., the alf_chroma_filter_signal_flag) can beinferred to be equal to 0.

A box (1101) in FIG. 11A indicates that the ALF chroma filter signalflag (e.g., the alf_chroma_filter_signal_flag) is signaled in the ALFdata syntax. A box (1102) in FIG. 11B indicates that when the ALF chromafilter signal flag (e.g., the alf_chroma_filter_signal_flag) is 1, ALFchroma filter information for the corresponding ALF chroma filter can beparsed. Referring to a box (1501) in FIG. 15 , the ALF chroma presentflag (e.g., the alf_chroma_present_flag) is signaled in an APS and canindicate whether a chroma component is present. Referring to a box(1601) in FIG. 16 , when the ALF chroma present flag (e.g., thealf_chroma_present_flag) is 1 indicating that the chroma component ispresent, the ALF chroma filter signal flag (e.g., thealf_chroma_filter_signal_flag) is signaled. Further, referring to a box(1602), when the ALF chroma filter signal flag (e.g., thealf_chroma_filter_signal_flag) is 1, the ALF chroma filter informationfor the corresponding ALF chroma filter can be parsed. Alternatively,when the ALF chroma present flag (e.g., the alf_chroma_present_flag) is0 indicating that the chroma component is not present, the ALF chromafilter signal flag (e.g., the alf_chroma_filter_signal_flag) is notsignaled. Subsequently, the ALF chroma filter information for thecorresponding ALF chroma filter is not parsed, and thus reducingsignaling overhead and improving coding efficiency.

FIG. 18 shows a flow chart outlining a process (1800) according to anembodiment of the disclosure. The ALF chroma filter as a chroma filtercan be disabled when the APS chroma present flag (e.g., theaps_chroma_present_flag) is 0, for example, to avoid an unnecessarydecoding process. Therefore, the ALF chroma filter signal flag (e.g.,the alf_chroma_filter_signal_flag) can be inferred to be 0.

In an example, the process (1800) starts at (S1801) and proceeds to(S1810).

At (S1810), whether the APS chroma present flag is 1 can be determined.When the APS chroma present flag is determined not to be 1, and thus achroma component is not present, the process (1800) proceeds to (S1820).Otherwise, when the APS chroma present flag is determined to be 1, theprocess (1800) proceeds to (S1830).

At (S1820), the ALF chroma filter signal flag can be inferred to be 0.The process (1800) proceeds to (S1840).

At (S1840), the ALF chroma filter is not applied to a chroma componentas the chroma component is not present. The process (1800) proceeds to(S1899), and terminates.

At (S1830), the ALF chroma filter signal flag can be decoded. Theprocess (1800) proceeds to (S1850).

At (S1850), whether the ALF chroma filter signal flag is 1 can bedetermined. When the ALF chroma filter signal flag is determined not tobe 1 (e.g., is 0), the process (1800) proceeds to (S1840). Otherwise,when the ALF chroma filter signal flag is determined to be 1, theprocess (1800) proceeds to (S1860).

At (S1860), the ALF chroma filter can be applied to the chroma componentthat is present. The process (1800) proceeds to (S1899), and terminates.

FIG. 19 shows a flow chart outlining a process (1900) according to anembodiment of the disclosure. In some examples, such as in VVC, certaincoding tools (e.g., BDPCM for chroma, palette mode coding, and ACT) areonly applied when the chroma format is 4:4:4 without separate colorplanes. Syntax elements related to the certain coding tools are notparsed when the chroma format is 4:4:4 with separate color planes (e.g.,the chroma component is coded as a luma component). Therefore, only whenthe chroma array type (e.g., the ChromaArrayType) equals to 3, thesyntax elements can be parsed to avoid an unnecessary decoding process.

In an example, the process (1900) starts at (S1901) and proceeds to(S1910).

At (S1910), whether the chroma array type is 3 can be determined. Thechroma array type being 3 can indicate the chroma format of 4:4:4without separate coding planes. When the chroma array type is determinednot to be the chroma format of 4:4:4 without separate coding planes, theprocess (1900) proceeds to (S1920). Otherwise, when the chroma arraytype is determined to be the chroma format of 4:4:4 without separatecoding planes, the process (1900) proceeds to (S1930).

At (S1920), a syntax element, such as the SPS BDPCM chroma enabled flag(e.g., the sps_bdpcm_chroma_enabled_flag), the SPS palette enabled flag(e.g., the sps_palette_enabled_flag), or the SPS ACT enabled flag (e.g.,a sps_act_enabled_flag), related to the chroma format of 4:4:4 withoutseparate color planes can be inferred to be 0. The process (1900)proceeds to (S1940).

At (S1940), a coding tool (e.g., the BDPCM, the palette coding, or ACT)related to the chroma format of 4:4:4 without separate color planes isnot applied. The process (1900) proceeds to (S1999), and terminates.

At (S1930), the syntax element related to the chroma format of 4:4:4without separate color planes can be decoded. The process (1900)proceeds to (S1950).

At (S1950), whether the syntax element is 1 can be determined. When thesyntax element is determined not to be 1 (e.g., equals to 0), theprocess (1900) proceeds to (S1940). Otherwise, when the syntax elementis determined to be 1, the process (1900) proceeds to (S1960).

At (S1960), the coding tool related to the chroma format of 4:4:4without separate color planes can be applied. The process (1900)proceeds to (S1999), and terminates.

When a chroma component is not present in a video bitstream, such asmonochrome or 4:4:4 with separately coded color planes, it is desirableto not decode chroma related syntax elements in high level syntax suchas a SPS, a PPS, an APS, a picture header and/or the like.

To ensure there are no conflicts in the signaling between the chromaarray type (e.g., the ChromaArrayType) and the related syntax elements,embodiments and/or methods in the disclosure can modify the SPS RBSPsyntax, PPS RBSP syntax, and/or ALF data syntax.

FIG. 20 shows an exemplary architecture (e.g., on a decoder side) of aluma mapping with chroma scaling (LMCS) coding tool according to anembodiment of the disclosure. In an example, such as in VVC, the LMCScoding tool is added as a new processing block before loop filters. TheLMCS coding tool can include two components: 1) in-loop mapping of aluma component based on adaptive piecewise linear models, 2)luma-dependent chroma residual scaling (CRS) that is applied to chromacomponent(s). A plurality of blocks (e.g., blocks (2011), (2012), and(2015)) can indicate where the processing is applied in the mappeddomain and can include an inverse quantization and inverse transformblock (2011), a luma intra prediction block (2015), and a reconstructionblock (2012) that can add a luma prediction Y′_(pred) together with aluma residual Y_(res). The luma prediction Y′_(pred) can be from theluma intra prediction block (2015) or a forward mapping block (2018) ofa luma signal Y_(pred). The luma signal Y_(pred) can be generated by amotion compensated prediction block (2016) that can have inputs from adecoded picture buffer (DPB) (2014). The DPB (2014) can be a buffer thatcan store decoded pictures.

A plurality of blocks (e.g., blocks (2002), (2003), (2005), (2006)) canindicate where the processing is applied in a non-mapped domain and caninclude loop filters (2003) such as deblocking, ALF, and SAO, a motioncompensated prediction block (2006), a chroma intra prediction block(2005), a reconstruction block (2002) that can add a chroma predictionC_(pred) together with a chroma residual C_(res), and storage of decodedpictures as reference pictures in a DPB (2004). LMCS functional blockscan include the forward mapping block (2018) of the luma signalY_(pred), an inverse mapping block (2017) of the luma signal, and aluma-dependent chroma scaling process block (2001). The inversequantization and inverse transform block (2011) can provide a chromaresidual scaling parameter (e.g., C_(resscale)) to the luma-dependentchroma scaling process block (2001). The luma-dependent chroma scalingprocess block (2001) can generate a chroma residual based on the chromaresidual scaling parameter (e.g., C_(resscale)) and a parameter (e.g.,cScaleInv). The parameter (e.g., cScaleInv) can be determined by thereconstruction block (2012) (e.g., based on reconstructed lumaneighbor(s), such as a top and/or a left neighbor of a current virtualpipeline data unit (VPDU)). An output of the inverse mapping block(2017) can be filtered by loop filters (2013) and then can be stored inthe DPB (2014). The LMCS coding tool can be enabled and/or disabled atthe sequence level using an SPS flag.

According to aspects of the disclosure, a first syntax element can bedecoded from a coded video bitstream. The first syntax element canindicate whether a first component in the coded video bitstream is codedbased on a second component in the coded video bitstream. Whether todecode one or more second syntax elements for a chroma related codingtool can be determined based on the first syntax element. The chromarelated coding tool can be a coding tool that is used only for chromacomponent(s) or a coding tool that uses chroma component(s). In someexamples, the chroma related coding tool is one of (i) the LMCS codingtool and (ii) a cross-component adaptive loop filter (CC-ALF).

The one or more second syntax elements for the chroma related codingtool can be decoded based on the first syntax element indicating thatthe first component is coded based on the second component in the codedvideo bitstream and the first component is a chroma component. The oneor more second syntax elements for the chroma related coding tool arenot decoded based on the first syntax element indicating that the firstcomponent is coded independently in the coded video bitstream, forexample, the first component is not coded based on the second componentin the coded video bitstream.

The first syntax element can be signaled in an APS. The first syntaxelement can be the APS chroma present flag (e.g., theaps_chroma_present_flag). The first syntax element can indicate at asequence level whether the first component is coded based on the secondcomponent.

The first syntax element can indicate whether a chroma component ispresent in the coded video bitstream.

When the first syntax element indicates that the first component iscoded based on the second component, the second component can be one ofa second chroma component and a luma component in the coded videobitstream. Accordingly, the chroma component (e.g., the first chromacomponent) is present in the coded video bitstream.

When the first syntax element indicates that the first component iscoded independently, for example, the first component is not coded basedon the second component, (i) the first component is the only componentin the coded video sequence or (ii) the coded video bitstream includesat least the first component and the second component and the firstcomponent is coded independently from the second component. Accordingly,the chroma component is determined not to be present in the coded videobitstream. For example, the coded video bitstream includes at least thefirst component and the second component that are coded independently.If the first component is a chroma component, the first component can beprocessed as a monochromatic component or a luma component without aneed to use the chroma related coding tool. Thus, a chroma component tobe coded based on another component in the coded video bitstream is notpresent.

In an example, the coded video bitstream includes a first chromacomponent, a second chroma component, and a luma component that have achroma format of 4:4:4. The first component is the first chromacomponent. The second component is the second chroma component or theluma component. The first chroma component, the second chroma component,and the luma component are coded independently from each other.

The chroma related coding tool can be disabled based on the first syntaxelement indicating that the first component is coded independently inthe coded video bitstream, for example, the first component is not codedbased on the second component in the coded video bitstream.

In an embodiment, the chroma related coding tool is the LMCS codingtool. The first syntax element can indicate that the first chromacomponent is coded based on the second component. The one or more secondsyntax elements for the LMCS coding tool can include a first LMCSparameter indicating an absolute value of a variable (e.g.,lmcsDeltaCrs) for LMCS chroma residual scaling (CRS). A second LMCSparameter for the LMCS coding tool can be decoded when the absolutevalue of the variable for the LMCS CRS is larger than 0. The second LMCSparameter can indicate a sign of the variable for the LMCS CRS. The oneor more second syntax elements can include the second LMCS parameter.The second LMCS parameter for the LMCS coding tool is not decoded whenthe absolute value of the variable for the LMCS CRS is not larger than0.

The LMCS is a residual scaling tool and can be applied to a lumacomponent and one or more chroma components. When a chroma component isnot present in the video bitstream, chroma related syntax elements(e.g., the first LMCS parameter, the second LMCS parameter) for the LMCScoding tool are not needed, for example, in an APS.

The first LMCS parameter (e.g., lmcs_delta_abs_crs) can specify anabsolute codeword value of the variable (e.g., lmcsDeltaCrs) for LMCSCRS. When the first LMCS parameter (e.g., lmcs_delta_abs_crs) is notpresent, the first LMCS parameter (e.g., lmcs_delta_abs_crs) can beinferred to be equal to 0.

The second LMCS parameter (e.g., lmcs_delta_sign_crs_flag) can specifythe sign of the variable (e.g., lmcsDeltaCrs). When the second LMCSparameter (e.g., lmcs_delta_sign_crs_flag) is not present, the secondLMCS parameter (e.g., lmcs_delta_sign_crs_flag) can be inferred to beequal to 0.

According to aspects of the disclosure, the chroma related syntaxelements (e.g., the first LMCS parameter, the second LMCS parameter) forthe LMCS coding tool may not be signaled. When the APS chroma presentflag (e.g., the aps_chroma_present_flag) is equal to 1, the chromacomponent is present (e.g., the chroma component is to be coded based onanother component in the coded video bitstream), and thus the chromarelated syntax for the LMCS coding tool can be signaled in a videobitstream. When the APS chroma present flag (e.g., theaps_chroma_present_flag) is equal to 0, the chroma component is notpresent and the chroma related syntax for the LMCS coding tool is notsignaled in the video bitstream. Thus, the chroma related syntax are notparsed or decoded by a decoder. Accordingly, signaling overhead can bereduced by not signaling the chroma related syntax elements for the LMCScoding tool when the chroma related syntax elements for the LMCS codingtool are not needed and coding efficiency can be improved.

FIG. 21 shows an exemplary LMCS data syntax according to an embodimentof the disclosure. Referring to a box (2101), whether the chroma relatedsyntax for the LMCS coding tool is signaled can be determined based onthe APS chroma present flag (e.g., the aps_chroma_present_flag). Whenthe APS chroma present flag (e.g., the aps_chroma_present_flag) is equalto 1, the chroma component is present. In an example, one chroma relatedsyntax element for the LMCS coding tool, such as the first LMCSparameter (e.g., the lmcs_delta_abs_crs) is signaled in a videobitstream. Whether to signal other chroma related syntax element(s) forthe LMCS coding tool can be determined based on the first LMCS parameter(e.g., the lmcs_delta_abs_crs). In an example, when the first LMCSparameter (e.g., the lmcs_delta_abs_crs) is larger than 0, the secondLMCS parameter (e.g., lmcs_delta_sign_crs_flag) that is a chroma relatedsyntax element for the LMCS coding tool is signaled. Otherwise, thesecond LMCS parameter (e.g., lmcs_delta_sign_crs_flag) is not signaled.

Referring to the box (2101), when the APS chroma present flag (e.g., theaps_chroma_present_flag) is equal to 0, the chroma component is notpresent. The chroma related syntax elements for the LMCS coding tool,such as the first LMCS parameter (e.g., the lmcs_delta_abs_crs) and thesecond LMCS parameter (e.g., lmcs_delta_sign_crs_flag), are not signaledin the video bitstream.

In an embodiment, the chroma related coding tool is the CC-ALF. Thefirst syntax element indicates that the first chroma component is codedbased on the second component. The one or more second syntax elementsfor the CC-ALF can include a first CC-ALF flag and a second CC-ALF flag.The first CC-ALF flag can indicate whether a first CC-ALF is signaled inthe coded video bitstream, and the second CC-ALF flag can indicatewhether a second CC-ALF is signaled in the coded video bitstream. Syntaxelements for the first CC-ALF can be decoded based on the first CC-ALFflag indicating that the first CC-ALF is signaled. The one or moresecond syntax elements for the CC-ALF can include the syntax elementsfor the first CC-ALF. The syntax elements for the first CC-ALF are notdecoded when the first CC-ALF flag indicates that the first CC-ALF isnot signaled.

Syntax elements for the second CC-ALF can be decoded based on the secondCC-ALF flag indicating that the second CC-ALF is signaled. The one ormore second syntax elements for the CC-ALF can include the syntaxelements for the second CC-ALF. The syntax elements for the secondCC-ALF are not decoded when the second CC-ALF flag indicates that thesecond CC-ALF is not signaled.

The CC-ALF is an ALF applied to chroma component(s). Chroma relatedsyntax elements for the CC-ALF can include the first CC-ALF flag (e.g.,an alf_cross_component_cb_filter_signal_flag) indicating whether thefirst CC-ALF is signaled in the coded video bitstream, the second CC-ALFflag (e.g., an alf_cross_component_cr_filter_signal_flag) indicatingwhether the second CC-ALF is signaled in the coded video bitstream, thesyntax elements for the first CC-ALF, the syntax elements for the secondCC-ALF, and/or the like.

The first CC-ALF flag (e.g., thealf_cross_component_cb_filter_signal_flag) being equal to 1 can specifythat the first CC-ALF (e.g., a cross component Cb filter) is signaled.The first CC-ALF flag (e.g., thealf_cross_component_cb_filter_signal_flag) being equal to 0 can specifythat the first CC-ALF (e.g., the cross component Cb filter) is notsignaled. When the first CC-ALF flag (e.g., thealf_cross_component_cb_filter_signal_flag) is not present, the firstCC-ALF flag (e.g., the alf_cross_component_cb_filter_signal_flag) can beinferred to be 0.

The second CC-ALF flag (e.g., alf_cross_component_cr_filter_signal_flag)being equal to 1 can specify that a second CC-ALF (e.g., a crosscomponent Cr filter) is signaled. The second CC-ALF flag (e.g., thealf_cross_component_cr_filter_signal_flag) being equal to 0 can specifythat the second CC-ALF (e.g., the cross component Cr filter) is notsignaled. When the second CC-ALF flag (e.g., thealf_cross_component_cr_filter_signal_flag) is not present, the secondCC-ALF flag (e.g., the alf_cross_component_cr_filter_signal_flag) can beinferred to be 0.

A chroma component not being present in a video bitstream can indicatethat each component in the video bitstream is coded independently as amonochromatic component or a luma component. Thus, the CC-ALF is notneeded for the component, and thus the chroma related syntax elementsfor the CC-ALF are not needed, for example, in an APS. Accordingly, thechroma related syntax elements for the CC-ALF may not be signaled.

When the APS chroma present flag (e.g., the aps_chroma_present_flag) isequal to 1, a chroma component is present, and one or more (e.g., thefirst CC-ALF flag, the second CC-ALF flag) of the chroma related syntaxelements for the CC-ALF can be signaled in the video bitstream. When theAPS chroma present flag (e.g., the aps_chroma_present_flag) is equal to0, the chroma component is not present, and thus the chroma relatedsyntax elements are not signaled in the video bitstream. Accordingly,signaling overhead can be reduced by not signaling the chroma relatedsyntax elements when the chroma related syntax elements for the CC-ALFare not needed and coding efficiency can be improved.

FIGS. 22A-22B show an exemplary ALF data syntax according to anembodiment of the disclosure. Referring to a box (2201), whether one ormore of the chroma related syntax elements for the CC-ALF are signaledin the video bitstream can be determined based on the APS chroma presentflag (e.g., the aps_chroma_present_flag). When the APS chroma presentflag (e.g., the aps_chroma_present_flag) is equal to 1, a chromacomponent is present, and the one or more (e.g., the first CC-ALF flag,the second CC-ALF flag) of the chroma related syntax elements for theCC-ALF can be signaled in the video bitstream.

Whether additional syntax elements of the chroma related syntax elementsfor the CC-ALF are signaled can be determined based on the one or more(e.g., the first CC-ALF flag, the second CC-ALF flag) of the chromarelated syntax elements for the CC-ALF. Referring to a box (2202), whenthe first CC-ALF flag is 1, the syntax elements for the first CC-ALF canbe signaled in the video bitstream, and thus can be parsed or decoded bya decoder. Referring to a box (2203), when the second CC-ALF flag is 1,the syntax elements for the second CC-ALF can be signaled in the videobitstream, and thus can be parsed or decoded by the decoder.

Referring back to the boxes (2201)-(2203), when the APS chroma presentflag (e.g., the aps_chroma_present_flag) is equal to 0, a chromacomponent is not present, and thus the chroma related syntax elementsfor the CC-ALF are not signaled in the video bitstream.

FIG. 23 shows a flow chart outlining a process (2300) according to anembodiment of the disclosure. The process (2300) can be used insignaling a chroma present flag (e.g., the APS chroma present flag, thePPS chroma present flag) to support various chroma format and chromarelated coding tools (e.g., the LMCS coding tool, the CC-ALF). Invarious embodiments, the process (2300) are executed by processingcircuitry, such as the processing circuitry in the terminal devices(310), (320), (330) and (340), the processing circuitry that performsfunctions of the video encoder (403), the processing circuitry thatperforms functions of the video decoder (410), the processing circuitrythat performs functions of the video decoder (510), the processingcircuitry that performs functions of the video encoder (603), and thelike. In some embodiments, the process (2300) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (2300). Theprocess starts at (S2301) and proceeds to (S2310).

At (S2310), a first syntax element can be decoded from a coded videobitstream. The first syntax element can indicate whether a firstcomponent in the coded video bitstream is coded based on a secondcomponent in the coded video bitstream.

At (S2320), whether to decode one or more second syntax elements for achroma related coding tool can be determined based on the first syntaxelement. The chroma related coding tool can be one of (i) a luma mappingwith chroma scaling (LMCS) coding tool and (ii) a cross-componentadaptive loop filter (CC-ALF). If the first syntax element indicatesthat the first component is coded based on the second component in thecoded video bitstream, the process (2300) proceeds to (S2330).Otherwise, if the first syntax element indicates that the firstcomponent is coded independently in the coded video bitstream, forexample, the first component is not coded based on the second componentin the coded video bitstream, the process (2300) proceeds to (S2399)without decoding the one or more second syntax elements for the chromarelated coding tool.

At (S2330), the one or more second syntax elements for the chromarelated coding tool can be decoded. The first component can be a firstchroma component. The first chroma component is present in the codedvideo bitstream. The process (2300) proceeds to (S2399) and terminates.

Decoding of the one or more second syntax elements for the chromarelated coding tool can be skipped when the chroma present is notpresent in the coded video bitstream. The chroma related coding tool isnot needed, and thus chroma related syntax elements for the chromarelated coding tool are not signaled in the coded video bitstream andare not decoded on a decoder side to reduce signaling overhead andimprove coding efficiency.

The process (2300) can be suitably adapted. Step(s) in the process(2300) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used. For example, when themaximum number of merge candidates does not satisfy the condition, thepicture level parameter is not decoded.

Embodiments in the disclosure may be used separately or combined in anyorder. Further, each of the methods (or embodiments), an encoder, and adecoder may be implemented by processing circuitry (e.g., one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 24 shows a computersystem (2400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 24 for computer system (2400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2400).

Computer system (2400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2401), mouse (2402), trackpad (2403), touchscreen (2410), data-glove (not shown), joystick (2405), microphone(2406), scanner (2407), camera (2408).

Computer system (2400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2410), data-glove (not shown), or joystick (2405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2409), headphones(not depicted)), visual output devices (such as screens (2410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2420) with CD/DVD or the like media (2421), thumb-drive (2422),removable hard drive or solid state drive (2423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2400) can also include an interface (2454) to one ormore communication networks (2455). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (2449) (such as,for example USB ports of the computer system (2400)); others arecommonly integrated into the core of the computer system (2400) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (2400) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2440) of thecomputer system (2400).

The core (2440) can include one or more Central Processing Units (CPU)(2441), Graphics Processing Units (GPU) (2442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2443), hardware accelerators for certain tasks (2444), graphicsadapters (2450) and so forth. These devices, along with Read-only memory(ROM) (2445), Random-access memory (2446), internal mass storage such asinternal non-user accessible hard drives, SSDs, and the like (2447), maybe connected through a system bus (2448). In some computer systems, thesystem bus (2448) can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus (2448), or through a peripheral bus (2449). In an example, thescreen (2410) can be connected to the graphics adatper (2450).Architectures for a peripheral bus include PCI, USB, and the like.

CPUs (2441), GPUs (2442), FPGAs (2443), and accelerators (2444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2445) or RAM (2446). Transitional data can be also be stored in RAM(2446), whereas permanent data can be stored for example, in theinternal mass storage (2447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2441), GPU (2442), massstorage (2447), ROM (2445), RAM (2446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (2400), and specifically the core (2440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (2440) that are of non-transitorynature, such as core-internal mass storage (2447) or ROM (2445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   -   JEM: joint exploration model    -   VVC: versatile video coding    -   BMS: benchmark set    -   MV: Motion Vector    -   HEVC: High Efficiency Video Coding    -   SEI: Supplementary Enhancement Information    -   VUI: Video Usability Information    -   GOPs: Groups of Pictures    -   TUs: Transform Units,    -   PUs: Prediction Units    -   CTUs: Coding Tree Units    -   CTBs: Coding Tree Blocks    -   PBs: Prediction Blocks    -   HRD: Hypothetical Reference Decoder    -   SNR: Signal Noise Ratio    -   CPUs: Central Processing Units    -   GPUs: Graphics Processing Units    -   CRT: Cathode Ray Tube    -   LCD: Liquid-Crystal Display    -   OLED: Organic Light-Emitting Diode    -   CD: Compact Disc    -   DVD: Digital Video Disc    -   ROM: Read-Only Memory    -   RAM: Random Access Memory    -   ASIC: Application-Specific Integrated Circuit    -   PLD: Programmable Logic Device    -   LAN: Local Area Network    -   GSM: Global System for Mobile communications    -   LTE: Long-Term Evolution    -   CANBus: Controller Area Network Bus    -   USB: Universal Serial Bus    -   PCI: Peripheral Component Interconnect    -   FPGA: Field Programmable Gate Areas    -   SSD: solid-state drive    -   IC: Integrated Circuit    -   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video encoding, comprising: settinga value of a first syntax element that indicates whether a chromacomponent is present in a video bitstream; determining whether to signalin the video bitstream one or more second syntax elements directed tochroma coding tools based on whether the chroma component is present inthe video bitstream; setting values of the one or more second syntaxelements directed to the chroma coding tools based on the chromacomponent being present in the video bitstream; and encoding the videobitstream including at least the first syntax element and the one ormore second syntax elements.
 2. The method of claim 1, wherein the firstsyntax element is signaled in an adaptation parameter set (APS) and theone or more second syntax elements are included in the APS.
 3. Themethod of claim 1, wherein the first syntax element is signaled in apicture parameter set (PPS) and the one or more second syntax elementsare included in the PPS.
 4. The method of claim 1, wherein the firstsyntax element includes an APS syntax element and a PPS syntax element,the one or more second syntax elements include a first subset of thesecond syntax elements and a second subset of the second syntaxelements, the APS syntax element is signaled in an adaptation parameterset (APS) and the first subset of the second syntax elements is includedin the APS, and the PPS syntax element is signaled in a pictureparameter set (PPS) and the second subset of the second syntax elementsis included in the APS.
 5. The method of claim 1, wherein, when thefirst syntax element indicates that the chroma component is not presentin the video bitstream, a chroma array type variable has a value thatindicates that the video bitstream is either monochromatic or has achroma format of 4:4:4 with separately coded color planes.
 6. The methodof claim 2, wherein the first syntax element indicates that the chromacomponent is present in the video bitstream; and the determiningcomprises determining to signal in the video bitstream a second syntaxelement indicating whether an adaptive loop filter (ALF) is signaled forthe chroma component.
 7. The method of claim 3, the first syntax elementindicates that the chroma component is present in the video bitstream;and the determining comprises determining to signal in the videobitstream plural second syntax elements, the plural second syntaxelements comprising at least one of (i) a variable indicating aquantization parameter (QP) offset, (ii) a variable indicating that ajoint CbCr QP offset list and a joint CbCr QP offset value are includedin the PPS, (iii) a variable indicating whether slice QP offsets arepresent in associated slice headers, or (iv) a variable indicatingwhether an intra slice syntax element and an inter slice syntax elementare present in picture headers referring to the PPS.
 8. An apparatus forvideo encoding, comprising: processing circuitry configured to set avalue of a first syntax element that indicates whether a chromacomponent is present in a video bitstream; determine whether to signalin the video bitstream one or more second syntax elements directed tochroma coding tools based on whether the chroma component is present inthe video bitstream; set values of the one or more second syntaxelements directed to the chroma coding tools based on the chromacomponent being present in the video bitstream; and encode the videobitstream including at least the first syntax element and the one ormore second syntax elements.
 9. The apparatus of claim 8, wherein thefirst syntax element is signaled in an adaptation parameter set (APS).10. The apparatus of claim 8, wherein the first syntax element issignaled in a picture parameter set (PPS) and the one or more secondsyntax elements are included in the PPS.
 11. The apparatus of claim 8,wherein the first syntax element includes an APS syntax element and aPPS syntax element, the one or more second syntax elements include afirst subset of the second syntax elements and a second subset of thesecond syntax elements, the APS syntax element is signaled in anadaptation parameter set (APS) and the first subset of the second syntaxelements is included in the APS, and the PPS syntax element is signaledin a picture parameter set (PPS) and the second subset of the secondsyntax elements is included in the APS.
 12. The apparatus of claim 8,wherein, when the first syntax element indicates that the chromacomponent is not present in the video bitstream, a chroma array typevariable has a value that indicates that the video bitstream is eithermonochromatic or has a chroma format of 4:4:4 with separately codedcolor planes.
 13. The apparatus of claim 9, wherein the first syntaxelement indicates that the chroma component is present in the videobitstream; and the processing circuitry is further configured to:determine to signal in the video bitstream a second syntax elementindicating whether an adaptive loop filter (ALF) is signaled for thechroma component.
 14. The apparatus of claim 10, wherein the firstsyntax element indicates that the chroma component is present in thevideo bitstream; and the processing circuitry is further configured to:determine to signal in the video bitstream plural second syntaxelements, the plural second syntax elements comprising at least one of(i) a variable indicating a quantization parameter (QP) offset, (ii) avariable indicating that a joint CbCr QP offset list and a joint CbCr QPoffset value are included in the PPS, (iii) a variable indicatingwhether slice QP offsets are present in associated slice headers, or(iv) a variable indicating whether an intra slice syntax element and aninter slice syntax element are present in picture headers referring tothe PPS.
 15. A non-transitory computer-readable storage medium storinginstructions which, when executed by processing circuitry, cause theprocessing circuitry to perform: setting a value of a first syntaxelement that indicates whether a chroma component is present in a videobitstream; determining whether to signal in the video bitstream one ormore second syntax elements directed to chroma coding tools based onwhether the chroma component is present in the video bitstream; settingvalues of the one or more second syntax elements directed to the chromacoding tools based on the chroma component being present in the videobitstream; and encoding the video bitstream including at least the firstsyntax element and the one or more second syntax elements.
 16. Thenon-transitory computer-readable storage medium of claim 15, wherein thefirst syntax element is signaled in an adaptation parameter set (APS).17. The non-transitory computer-readable storage medium of claim 15,wherein the first syntax element is signaled in a picture parameter set(PPS) and the one or more second syntax elements are included in thePPS.
 18. The non-transitory computer-readable storage medium of claim15, wherein the first syntax element includes an APS syntax element anda PPS syntax element, the one or more second syntax elements include afirst subset of the second syntax elements and a second subset of thesecond syntax elements, the APS syntax element is signaled in anadaptation parameter set (APS) and the first subset of the second syntaxelements is included in the APS, and the PPS syntax element is signaledin a picture parameter set (PPS) and the second subset of the secondsyntax elements is included in the APS.
 19. The non-transitorycomputer-readable storage medium of claim 15, wherein, when the firstsyntax element indicates that the chroma component is not present in thevideo bitstream, a chroma array type variable has a value that indicatesthat the video bitstream is either monochromatic or has a chroma formatof 4:4:4 with separately coded color planes.
 20. The non-transitorycomputer-readable storage medium of claim 15, wherein the first syntaxelement indicates that the chroma component is present in the videobitstream; and the instructions further cause the processing circuitryto perform: determining to signal in the video bitstream a second syntaxelement indicating whether an adaptive loop filter (ALF) is signaled forthe chroma component.